1. Field of the Invention
The present invention relates to a backlight for a liquid crystal display (LCD) using a light emitting diode, and more particularly, to an LCD backlight unit using a light emitting diode which is free from a problem of darkness caused in an area of an LCD panel corresponding to a connector equipped in the backlight unit to electrically connect a plurality of independently-driven LED modules to achieve local dimming.
2. Description of the Related Art
A cold cathode fluorescent lamp (CCFL) has been conventionally utilized as a light source of a light crystal display (LCD) backlight. The CCFL may trigger environmental pollution due to use of a mercury gas. Also, the CCFL is low in response rate and color reproducibility, and inadequate for reducing the weight and size of an LCD panel.
In contrast, a light emitting diode (LED) is environment-friendly and can respond fast with several nano seconds, thus effective in video signal stream. Moreover, the LED can be impulsively driven, reproduce colors by 100% or more and arbitrarily change brightness and color temperature by adjusting a light amount of red, green and blue LEDs. Also, the LED carries advantages leading to a lighter weight and smaller sized LCD panel. Thus the LED is actively adopted as a backlight source of the LCD panel.
In general, the LCD backlight employing the LEDs includes an edge-type backlight and a direct-type backlight depending on location of a light source. In the former, a light source is shaped as an elongated bar and disposed at a side of a light guide plate to irradiate light onto the LCD panel. In the latter, a surface light source is substantially identical in size to the LCD panel and disposed under the LCD panel to directly irradiate light onto the LCD panel. Especially, the direct type backlight unit directly irradiates light from just below the LCD panel. This advantageously allows light to be irradiated with different brightness onto some portion of the LCD panel, thereby achieving local dimming.
With such local dimming, a signal of an image to be displayed on the LCD panel is analyzed to find an area to be brighter or dimmer, and the brightness of a corresponding area of the backlight is controlled based on the analysis. This technology accordingly imparts more vividness to the image provided through the LCD panel. For example, in the image of explosion, brightness of the backlight source disposed just below an area of the LCD panel displaying such explosion can be increased through the local dimming, thereby ensuring more life-likeness and vividness to the scene.
FIG. 1a is a plan view illustrating a conventional LCD backlight used for local dimming. FIG. 1b is a partial cross-sectional view illustrating the LCD backlight cut along the line a-a′. Referring to FIGS. 1a and 1b, the conventional LCD backlight 10 for local dimming uses a combination of LED modules M1 to M12, each of which is designed to illuminate light onto a corresponding portion of an LCD panel. Each of the LED modules M1 to M12 includes a plurality of LEDs 121 disposed on a printed circuit board (PCB) 11. Each of the LED modules M1 to M12 may include at least one respective red, green and blue LEDs to produce white light. Also, out of the LEDs 121 in the LED module M1 to M12, the LEDs of the same color are electrically connected with one another. For this electrical connection, first lead patterns (not illustrated) are formed on some areas of the PCB where the LEDs are not disposed.
Each of the LED modules M1 to M12 is independently driven to illuminate light of different brightness, thereby implementing local dimming. To this end, a plurality of driving circuits are provided to drive the LED modules M1 to M12, respectively. Each of the LED modules M1 to M12 should be electrically connected to a corresponding one of the driving circuits. To ensure electrical connection with the external driving circuits, driving circuit connectors 15 are disposed in the LED modules M1, M5, and M9, respectively, in an outermost periphery of the backlight 10, which is the leftist side in FIG. 1. Here, in each of the LED modules M1, M5 and M9 located in the leftist side of the backlight, each of the first lead patterns is directly connected to a corresponding one of the driving circuit connectors 15. However, the LED modules M2 to M4, M6 to M8 and M10 to M12 located right from the LED modules M1, M5 and M9 cannot be directly connected to the driving circuit connectors 15, respectively. Thus the LED modules M1 to M12 are connected to the adjacent ones thereof through module connectors 13. For example, note the LED modules (first modules) M1, M5 and M9 located in the leftist side and the LED modules (second modules) M2, M6 and M10 located right next thereto in FIG. 1a. As described above, each of the first modules M1, M5, and M9 should be provided with the lead pattern for connecting the LEDs on the PCB 11. Besides, the first modules 1, M5, and M9 should be provided with second lead patterns for each connection between the corresponding one of the module connectors 13 and the corresponding one of the driving circuit connectors 15 thereby to be connected with a corresponding one of the second modules M2, M6 and M10. The second lead patterns connecting the LEDs of the second modules M2, M6, M10 on the PCB are connected to the first lead patterns of the first modules M1, M5, M9 through conductive lines 14 of the module connectors 13, thereby electrically connected to the driving circuit connectors 15. In a similar manner, the LEDs in each of the modules M3, M7, M11 located next to the right from the second modules M2, M6, M10 are eventually connected to the corresponding one of the driving circuit connectors 15 through the module connectors and the second lead patterns formed on the LED modules next to the left from the LED modules M3, M7 and M11.
In the conventional LCD backlight 10 for local dimming configured as above, the LED modules M1 to M12 should be provided with not only the first lead patterns for connecting the LEDs 121 disposed in each of the LED modules but also the second lead patterns for connecting the adjacent LED modules with the driving circuit connectors 15. This disadvantageously complicates a wiring configuration. Notably, in a case where the backlight adopts small LEDs, a great number of LEDs should be disposed densely on the PCB, thus very hard to secure a space for forming the first and second lead patterns.
Also, as shown in FIG. 1b, the module connectors 13 for electrically connecting the LED modules and the conductive lines 14 are formed higher than the LEDs 121. Accordingly light generated from the LEDs 121 are blocked by the module connectors 13 and conductive wires 14. This causes darkness in an area D of an LCD panel corresponding to the module connectors 13, thereby hindering proper illumination.